Tamper resisting fuse



Jan. 20, 1953 G. VON HOQRN 2,626,300

TAMPER RESISTING FUSE Filed Nov. 10, 1950 v Inventor:

Fred G. o H o, b

His Attovn Patented Jan. 20, 1953 TAMPER RESISTING FUSE Fred G. von- Hoorn, Nichols, Conn., assignor to General Electric Company,v a corporation: of

New York ApplicationiNovember. 10, 1950, Serial No. 194,967

1Claim, 1

This. invention. relates to. tamper'resisting plug fuse adapters.

Householdv circuits; are so constructed. that they are safely limited to the carrying of a predetermined current. For example, acertain household circuit might be safely limited to Iii-ampere capacity while another circuit might be capable of safely carrying 30 amperes. The size and type of wire in each circuit will determine the load ca pacity..

To insure the limiting of current in these circuits to their safe boundaries, fuses are installed in the circuit which will blow if an overcurrent is passed therethrough. Unfortunately, however, heretofore it has. been possible to install a 30 ampere: fusein a circuit that had been designed to carry 15 amperes. Obviouslythis is a dangerous condition that should be avoided.

To solve this problem, manufacturers in the past have provided adapters which are usually an, insulating disk threadable into a plug fuse holder, the; adapter having an aperture axially therein to allow only a fuse. of a predetermined size to pass through the aperture to make contact in the fuse holder.

While adapters of this sort have been known and while these have been both lockable adapters which can be permanently installed in a fuse holder or removable adapters which can be removably inserted in a fuse holder, it is sometimes desirable to have an adapter which may be either lockable or temporarily installable in a fuse holder. It is an object of this invention, therefore, to provide a new and improved adapter for tamper resisting plug fuses which is insertable into a fuse holder either to be permanently secured therein or to be removable.

It is a further object of this invention to provide a new and improved adapter for tamper resisting plug fuses.

It is a still further object of this invention to provide a new and improved adapter for plug fuses that may be readily changed from a lockable to a removable adapter or vice versa.

Further objects and advantages of this invention will become apparent and the invention will be more clearly understood from the following description referring to the accompanying drawing, and the features of novelty which characterize this invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

Broadly, this invention comprises the combination of an insulating plastic disk having a screw thread in its outer periphery and a groove for housing a springrdetent for securing the adapter in a fuseholder. This spring detent is removably secured.

Referring to the drawing, Fig. l is a front elevation, partly in section, of a fuse holder containing a plug fuse therein; Fig. 2 is an end elevation of the adapter; while Fig. 3 is a front elevation of the new and improved adapter.

In the drawing a fuse holder l is shown comprising a base 2, a threaded shell 3 and a center tap screw or contact 4. A plug fuse on the other hand is shown in this example as comprising a glasstbody portion 5 having a threaded shell engaging'cartridge 5 and cylindrical end i engageable with the threaded center contact l. An adapter 8, on the other hand, is shown as comprising aplastic body portion fi having a threaded outer periphery Ill and a central aperture ll registeringv with the center contact 6 and the cylindrical portion 1 on the plug fuse so that the cylindrical portion can pass through the adapter and engagethe center contact 4.

The central aperture H is designed to have a predetermined diameter. Specifically, an adapter for-a 15-ampere'fuse, for example, would have one diameter and for a 30-ampere fuse would have a larger diameter. Then the fuse itself would have a cylindrical end portion l so that a iii-ampere fuse would have cylindrical end I registering with the l5-ampere adapter bore H and the SO-ampere fuse would have a cylindrical end 1 registrable with the BO-ampere bore II. It is obvious, therefore, that the l5-ampere fuse will be insertable through the bore H of either the 15-ampere adapter or the 30-ampere adapter. On the other hand, a 30-ampere fuse, since it has a larger cylindrical end i, will not be insertable through a 15-ampere adapter. Consequently, the overloading of the l5-ampere circuit will be prevented.

The adapter 8 is provided centrally with ratchet like notches [2 which can accommodate a tool (not shown) for tightening the adapter axially into the fuse holder. Another and more important purpose of the notches I2 is to prevent tampering with a blown fuse. For example, assume that a fine wire or similar conductor has been attached to the underside of a blown fuse to form a conducting bridge between the center contact I I and the outer screw shell and that the tampered fuse is then turned into the fuse holder to establish a circuit. The oppositely disposed telescoping projections of the fuse and adapter cause the wire to be drawn over the notches l2 and severed as the fuse is being turned into the holder. Adapter 8 is further provided with raised threaded portions I0 engageable with the threaded shell 2 as heretofore mentioned; and furthermore it is provided with radial grooves or notches I 4 and i 5 plus a peripheral groove 01' notch I6, all of which grooves or notches are engageable with a spring locking device ll. Locking device 17 comprises a semi-circular piece of spring wire having a bent or hook portion ill on one end and a looped portion IS on the other end with a projection forming a pin point or barb 20 extending outwardly therefrom to be engageable with the screw shell 3. Specifically, the hook portion l8 engages complementary groove l4 while the body portion of the wire extends through the groove 15 and the looped end [9 engages the other groove 15. With this structure, the pin point 28 extends tangentially out from the adapter.

The groove I5 is so constructed that when the adapter is turned clockwise as seen in Fig. 2, the barb 2B is depressed into the groove 15 to allow for the clockwise turning of the adapter; if the adapter is turned counterclockwise, however, the barb Eil extends outward from the adapter and engages the screw shell 3 of the fuse holder, thus preventing the counterclockwise turning of the adapter.

An important feature of this invention is that the spring locking device 1? is readily removable. It is apparent from the drawing that the two notches I4 and [5 are spaced substantially 180 apart and that when the two ends of the spring engage these notches respectively, the spring is substantially locked in place. However, by moving the loop portion [9 of the spring radially outwardly, the whole spring is disengageable from the adapter and removable from the groove It.

With this structure, it is obvious that the spring locking device I! may be either installed on or removed from the adapter whereby the adapter may be used either in a removable or in a locked fashion depending on whether or not the spring locking device is used.

Modifications of this invention will occur to 4 those skilled in the art and it is desired to be understood, therefore, that this invention is not intended to be limited to the particular embodiment disclosed but that it is intended to cover all modifications which are within the true spirit and scope of this invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

The combination of an adapter for limiting the type of fuse insertable into a plug fuse socket and removable locking means for efiecting (when used), the locking of said adapter in a fuse socket, said adapter having a circumferential thread engageable with said fuse socket, a circumferential groove adjacent said thread, and a pair of oppositely disposed radially inwardly extending grooves one located at each end of said circumferential groove, said removable means comprising an arcuately shaped spring locking device removably engageable with said grooves, said locking device having a radially inwardly extending projection on one end engageable with one of the radially inwardly extending grooves and a hook shaped portion at its other end to provide a radially inwardly extending section for engaging said second radial groove in said adapter and a tangentially outwardly extending section resiliently depressible into said second radial groove when the adapter is turned clockwise and engageable with said fuse socket to prevent the counterclockwise rotation of said adapter.

FRED G. VON HOORN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 959,818 Timm May 31, 1910 994,854 Maokin June 13, 1911 2,115,447 McEntee Apr. 26, 1938 

